A. Field of the Invention
This invention relates to inspection for flaws of any surface that is smooth enough to provide a reflection. One particular example is surfaces such as painted surfaces on such things as, for example, automobile bodies and the like where the paint or the underlying surface are inspected for flaws, the invention relates to both an apparatus and method by which such inspections takes place, including but not limited to along an automated production line.
B. Problems in the Art
Most automobile manufacturers use robotics and an automated painting system to apply various coats of paint to create the paint surface on the automobile bodies that are then used to create the complete automobile. While such systems generally perform satisfactorily, most manufacturers have a quality review of the paint job prior to approving the painted car body for assembly into the completed car.
One conventional quality control review involves workers manually moving around each automobile body as it moves along a conveyor and visually scanning the automobile body for a number of different possible flaws.
The workers are generally given only a short time (for example only several minutes) to evaluate the entire automobile body. Generally, the industry has constructed a paint inspection station that has sufficient room for the workers to walk around each car body. Importantly, the state of the art provides as much direct light as possible to the car bodies during the inspection process. The theory is apparently that the more light the better to visually identify flaws. The emphasis is on lighting the car body.
The inspection workers must watch for as many as several tens of different types of flaws or defects. For example, if there is an underlying flaw such as a raised portion or recessed portion in the car body metal, this will normally be reflected in a raised or recessed portion respectively in the paint job. Also, such things as dust or other particles that may have settled on the car body prior to or during painting will result in a noticeable flaw.
Presently, automobile paint jobs are multi-coat. For example, a first coat or a neutral color rust inhibitor of fairly matte finish (sometimes called an "E" coat), is applied to the metal. A primer coat, usually neutral with a somewhat matte finish or the same color as the ultimate car color, is applied to the first coat. Finally, one or more top coats, for example, a base coat plus a clear coat can be applied over the primer coat.
The inspector analyzes the first coat for such things as uniformity, flaws and foreign materials. The primer coat is analyzed for such things as flaws, eveness, uniformity, dirt, cavities, runs, and negative or positive depressions in the metal. The top coat creates a highly reflective surface which is inspected for such things as eveness, white spots, striations, swirl marks and other flaws.
If a flaw is identified, the workers attempt to polish it out on the spot, or the car body must be towed from the assembly line to another location for paint repair. It should be understood that if the repairs are substantial, whole sections of the body may have to be repainted. When the body is then passed again through the paint inspection station, a further important evaluation involves whether the repainted portion matches the rest of the car with respect to color, in addition to looking for the other flaws and for blending and eveness.
Bathing the car bodies in light does arguably help in identifying certain flaws, but the problems with such an approach include the following. To bathe the car body in so much direct light with so many fixtures adjacent the car body can wash out or minimize the visual perception of certain flaws. Additionally, glare from light fixtures that are projecting light towards the inspector can reduce the ability to accurately analyze the paint job. Moreover, reflections of the fixture's direct light from the car body makes it many times difficult to identify flaws and can cause glare and difficulty in concentrating on the inspection and upon insuring that all portions of the car body are examined carefully.
Moreover, so much direct light can also make it very difficult to analyze color matching. With clear coated paint jobs, the highly reflective nature of the paint coating increases the problems of having so much direct light to the car body. Also, by bathing the entire paint inspection area in light, it eliminates any contrast between the car body and the surrounding areas.
Several United States patents exist which address the issue of inspecting paint jobs. U.S. Pat. No. 4,918,321 to Klenk, et al. discloses a completely automated inspection system. Live inspectors are not used. Sensors, including video cameras, receive reflected light from the vehicle surface and a computer controls a scanning mirror so that the vehicle body is essentially scanned for flaws. The computer must analyze the video image. Direct light is provided to the vehicle body.
U.S. Pat. No. 3,609,044 to Murphy is an apparatus for inspection of a specular surface and a coating on the surface. A reference pattern is projected onto the surface being inspected for detection of defects. In this instance light through the projected pattern is directly sent to the object's surface.
U.S. Pat. No. 4,629,319 to Clarke, et al. also utilizes the projection of a grid of light to a panel for detection of defects in sheet metal or plastic panels.
As previously discussed, the method of projecting light directly to the object being inspected carries with it deficiencies which impact upon the accuracy of the inspection. It is therefore a principle object of the present invention to provide an apparatus and method for paint inspection which improves over or solves the problems and deficiencies in the art.
Objects of the Invention Include:
1. Reduction of glare during the inspection process.
2. Reduction in the amount of light and illumination directly to the object of inspection and, in fact, intentionally removing direct light to the object and reducing ambient light.
3. Allowance of improved inspection for the variety of flaw types.
4. Allowance for inspection of different colors and types of paint jobs.
5. Assistance in the ability to concentrate and comprehensively cover the entire surface of the object under inspection.
6. Reduction in any washing out or lack of contrast between the object being inspected and the surroundings.
7. An economical setup in terms of both material, operating, and labor costs.
8. A flexible and adjustable system for different objects and coatings including different object shapes.
These and other objects, features, and advantages of the present invention will become more apparent with reference to the accompanying specification and claims.